Preparation of polyethylene in a two zone reactor employing caprylyl peroxide in the first zone as the catalyst



United States PatentC M PREPARATION OF POLYETHYLENE IN A TWO ZONEREACTOR EMPLOYENG CAPRYLYL PER- OXIDE IN THE FIRST ZONE AS THE CATALYSTSamuel B. Vaughn, In, and Hugh 5. Hagemeyer, .lr., Lougview, Tex.,assignors to Eastman Kodak Company, Rochester, N.Y., a corporation ofNew Jersey No Drawing. Continuation of application Ser. No. 861,453,Dec. 23, 1959. This application .iuly 30, 1962, er. No. 213,124

12 Claims. (Cl. 260-94.9)

This invention relates to a novel process for the polymerization ofethylene and, more particularly to the use of an organic peroxide insuch a process. In a specific aspect, this invention relates to a noveltwo-zone process for the polymerization of ethylene in the presence ofan organic peroxide catalyst.

Polyethylene has been described rather extensively in the literature,and it has been produced commercially in a variety of types havingdistinct properties. These different types of polyethylene have beenseparately classi fied and distinguished primarily by the density of thepolymer. The first type of polyethylene that was produced commerciallywas of the so-called low density type. This type of polyethylene hasbeen produced for some years in accordance with the process described byFawcett et al. in US. Patent No. 2,153,553. This low density form ofpolyethylene is usually regarded as having a density within the range of0.90 to 0.935 and, because of the high content of amorphous polymer,this type of polyethylene has relatively low hardness, low stiffness andlow melting point when compared with more highly crystalline ethylenepolymers. Many variations of the Fawcett et al. process have beenperformed in an attempt to modifythe product properties. Such variationsinclude the use of various reactor designs, catalysts and chain transferagents.

Due to the unique properties of polyethylene this polymer isparticularly useful in the film and packaging field and, for such uses,the low density form of polyethylene as contrasted with the medium andhigh density forms form of a film has not possessed the desiredtransparency and clarity for some uses in the film and packaging field.Numerous suggestions have been made for improving the clarity andtransparency of low density polyethylene but none of these have beencompletely satisfactory.

Accordingly, it is an object of this invention to provide a new processfor the preparation of low density polyethylene.

It is a further object of this invention to provide a new process forthe preparation of low density polyethylene in the presence of anorganic peroxide catalyst.

Another object of this invention is to provide a process capable ofproducing new low density ethylene polymer which is suitable for use inthe packaging field.

Another object of this invention is to provide a process for preparinglow density ethylene polymer having higher film transparency and gloss,lower film haze and blocking, and higher stiffness and softening pointthan the low density ethylene polymers now being produced.

In accordance with this invention, it has been found that low densityethylene polymers having excellent characteristics for use in the filmand packaging field can be 3,178,404 ?atented Apr. 13, 1965 produced bypolymerizing ethylene in two stages or zones using caprylyl peroxide asthe catalyst in the first stage or zone. In practicing this invention,ethylene is polymerized in two zones at a temperature in the range ofabout to 270 C., the catalyst in the first zone comprising caprylylperoxide, the temperature in said zone being substantially less thanthat in the second zone, and the pressure throughout said polymerizationbeing greater than about 500 atmospheres.

It is believed that this is the first use of caprylyl peroxide as acatalyst under the reaction conditions set forth in the basic Fawcett etal. patent referred to previously. Furthermore, until the presentinvention, no one has endeavored to employ caprylyl peroxide in a twozone polymerization procedure under the conditions which are describedin that patent. Moreover, as will be shown by the followingspecification, polyethylene can be produced in higher yields, based onthe catalyst, than those yields now being produced using a conventionalcatalyst such as lauroyl peroxide and, because of the solubility andstability of the catalyst, smaller and less complicated catalysthandling facilities are possible.

The catalyst employed in the practice of this invention has beendescribed by Doehnert and Mageli (D. F. Doehnert and O. L. Mageli,Evaluation of Organic Peroxides on the Basis of Half-Life Date.Preliminary copy of paper presented at the 13th Annual Meeting of theReinforced Plastics Division) as having the following general formula:

In conducting our polymerization reaction we feed the catalyst into thereaction zone in solution in a suitable solvent or diluent. The natureof the organic vehicle employed is subject to considerable variation.The wellknown inert liquid hydrocarbons are desirably employed. Catalystconcentrations of 5 to 50 Weight percent in mineral oil and 20 weightpercent in a relatively low boiling solvent can be used to greatadvantage when feeding catalyst into the reaction zone. Due to theexcellent solubility of the caprylyl peroxide the 50 weight percentsolution can be used even at room temperature. This is of greatcommercial importance in that fewer expensive catalyst pumps must beused and heated catalyst handling facilities are unnecessary. The amountof catalyst employed will vary with the conditions utilized and includesthose conventional catalytic amounts known to those skilled in the art.

As'pointed out-hereinbefore, the process of this inven tion is carriedout as a two-step or two-zone reaction. The temperature throughout thispolymerization process is maintained within the range of about 130 C. to270 C. and, more preferably,'within the range of about 130 to 250 C. Thetemperature in the first zone can be maintained within the range ofabout 130 to about 190 C., and more preferably within the range of aboutto C., while the temperature in the second zone is substantially greaterand can be maintained within the range of about 190 to about 270'C., andmore preferably, within the range of about 190 to about 250 C.

, The pressure employed throughout the ethylene polymerization processof this invention is maintained at 500' atmospheres or more, a preferredrange being about 500 to about 3000 atmospheres.

In carrying out a typical two-stage or two-zone reaction processethylene is fed into the first reaction zone at 10-60 C. and thetemperature in the first reaction zone is within the range of 130-490 C.The preferred range is 150-190 C. as measured at the center of the firstzone, and since the reaction is exothermic, suitable coolwhich are 3 ingmeans are usually required to maintain the desired temperature.

In a stirred vessel the agitation is chosen so that a maximum of backmixing takes place in the first reaction zone. This can usually beaccomplished by employing a single paddle or flat-bladed turbineagitator in the upper portion of the reaction zone.

The ethylene polymer stream is then passed to a second zone where asecond and different peroxygen type catalyst can be fed in with orwithout additional ethylene. Catalysts suitable for the second reactionzone are chosen from the group represented by organic peroxygen typefree-radial polymerization catalysts and include di-tertiary butylperoxide, p-menthane hydroperoxide, t-butyl peroxyisobutyrate,di-t-butyl diperphthalate, t-butyl peracetate, l-butyl perbenzoate,dicumyl peroxide, t-butyl hydroperoxide, diisobutyryl peroxide, methylethyl ketone peroxide, benzoyl peroxide, acetyl peroxide, laurylperoxide, and the like.

The temperature in the second reaction zone varies from about 190 C. inthe beginning or top of the reaction zone to about 270 C. in thedischarge end or bottom of the reaction zone. In a stirred vessel thedesign is chosen so as to substantially eliminate any back mixing intothe first reaction zone. This can be accomplished by means of a bafflebetween zones in a single reactor together with directional agitation inthe second reaction zone.

The process of this invention can be conducted in a single reactorhaving separate reaction zones preferably separated by a baffle or otherseparation means. This type of two-zone reactor is preferred for ourprocess. However, the two separate reactions forming our process can beconducted in separate reactors and alternatively the entire processcould be carried out in an elongated tubular reactor.

A chain transfer agent can be used to allow polymer of usable melt indexto be produced at a low reaction temperature. Chain transfer agentsother than propane, which is employed in Example 4, which can be used inthe polymerization of ethylene include for example: hydrogen;hexachloroethane; carbon tetrachloride; chloroform; saturatedhalogenated carboxylic acids and their esters, for example,dichloroacetic acid and its ethyl ester; aldehydes, for example,acetaldehyde; alkyl esters of inorganic oxyacids of sulfur, phosphorusor silicon, for 'example, diethyl sulphite, triethyl orthophosphate andtetrabutyl orthosilicate respectively; and mercaptans, for exampledodecyl mercaptan.

The following examples will demonstrate the process of polymerizingethylene in accordance with this invention without being restrictedthereto. These examples were performed in a single continuous two-zonereactor in which mixing between the two zones was kept to a minimum sothat the polymer is produced at two different reaction temperatures.

EXAMPLE 1 Ethylene was compressed and fed to a two-zone pressure vesselfitted with a stirrer, means for controlling the temperature andsuitable inlets and outlets to allow the continuous introduction ofreactants and continuous discharge of products. The reactor pressure wasadjusted to 1120 atmospheres. The temperature of the ingoing ethylenewas 39 C. with a top zone reaction temperature of 175 C. and a bottomzone reaction temperature of 225 C. With an over-all ethylene feed rateof 6,450 pounds per hour, 17.8 pounds per hour of a solution comprising13 weight percent caprylyl peroxide in mineral oil is fed in as the topzone catalyst. Additional ethylene and 41 pounds per hour of a solutioncomprising 5 weight percent ditertiary butyl peroxide in mineral oil wasfed to the second reaction zone.

Under these reaction conditions 1290 pounds per hour of product wereproduced which amounted to a yield of 574 pounds of polyethylene perpound of top zone catalyst and 6300 pounds of polyethylene per pound ofbottom zone catalyst.

The product properties are shown in Table I and are compared to aproduct made in the same equipment using untreated lauroyl peroxide(Example 7). The product of this example showed great improvement infilm transparency, gloss, and haze and was similar to the control samplein all other respects. Of great commercial significance is thethree-fold increase in yield.

EXAMPLE 2 Ethylene was compressed and fed to a two-zone pres sure vesselas in Example 1. The reactor pressure was adjusted to 1160 atmospheres.The temperature of the ingoing ethylene was 43 C. with a top zonereaction temperature of C. and a bottom zone reaction temperature of 260C. With an over-all ethylene feed rate of 6450 pounds per hour, 3.5pounds per hour of a solution comprising 50 weight percent caprylylperoxide in mineral oil is fed in as the top zone catalyst. 3.2 poundsper hour of a solution comprising 5 weight percent ditertiary butylperoxide in mineral oil was fed to the second reaction zone.

Under these reaction conditions 1310 pounds per hour of product wereproduced which amounted to a yield of 750 pounds of polyethylene perpound of top zone catalyst and 8200 pounds of polyethylene per pound ofbottom zone catalyst.

As can be seen from Table I, the film transparency, haze, and gloss weregreatly improved over the control material. There was a good improvementin film blocking, a further increase in the yield as well as a higherstiffness and Vicat softening point.

EXAMPLE 3 This example is similar to Example 2 as shown by Table Iexcept that the catalyst solvent was changed to a low boilinghydrocarbon which is extracted from the molten product by the recyclegas stream.

As seen from Table I, the product shows an increase in stiffness andVicat softening point over the material in Example 2. In addition, thefilm made from the material was almost nonblocking even with the highfilm transparency.

EXAMPLE 4 This run was performed at quite different reactor conditionseven though the same catalyst and equipment was used. The catalystsolution comprised 13 weight percent caprylyl peroxide in mineral oil.Propane was used as a chain transfer agent to make possible a 2 meltindex material at 1440 atmospheres pressure and 173 C. temperature. Nobottom zone catalyst was added, however, there was some catalyst carriedthrough from the top zone.

The film properties of the polyethylene polymers were still muchimproved over the control material made in the same equipment.

EXAMPLE 5 This example was performed in the same manner as the previousexamples, however, the top zone catalyst was 5 weight percent t-butylperbenzoate in mineral oil. The reactor pressure was 1195 atmospheresand the minimum top zone temperature attainable was 230 C. because ofthe low activity of the catalyst.

The use of t-butyl benzoate gave a product having poor opticalproperties, as shown in Table I, and was included to show the uniquefeatures of caprylyl peroxide.

EXAMPLE 6 This run was similar to the previous example except that 5weight percent t-butyl peracetate was used as the catalyst. A somewhatlower top zone temperature was possible but the optical properties ofthe film made from the product were still very poor.

EXAMPLE 7 Ethylene was polymerized in the same manner as in the previousexamples under the conditions set forth in Table I with the exceptionthat untreated lauroyl peroxide was employed as the top zone catalyst.

Table I shows the poor optical properties of the film made from thisproduct.

6 of about 190 to about 250 C., the pressure throughout the reactionbeing greater than about 500 atmospheres. 4. Process for thepolymerization of ethylene which comprises initially polymerizingethylene in the presence Table I REACTION CONDITIONS AND PRODUCTPROPERTIES Examples Control Reaction Pressure, Atm 1, 190 1, 120 1, 1601, 160 1, 440 1, 195 1, 075 1, 100 Incoming Ethylene Temp., C 41 39 4337 42 44 41 38 Reaction Temperature:

Top Zone, C 174 175 160 160 173 230 210 190 Bottom Zone, C 252 255 260260 202 249 249 250 Rates Per Hour:

Pounds Ethylene Fed 8, 900 6, 450 6, 450 6, 570 6, 300 5, 400 5, 500 9,000 Pounds Polyethylene Produced-.- 1, 780 1, 290 1, 310 1, 330 950 1.030 960 1, 810 Pounds I.Z. Catalyst Solution Fed 124 17. 8 3. 5 8. 412.1 10.8 Dhi 25. 1

a a Pounds B.Z. Catalyst Solution Fed 5. 6 4. 1 3. 2 3. 2 None 5, 1 Dlio5. 7

a a Catalyst Concentration:

Top Zone in the Solvent, Wt. Percent 8 13 50 20 13 5 18 Bottom Zone- 5 55 5 None 5 5 5 Yield-Pounds of Polyethylene per pound of:

I.Z. Catalyst 180 574 750 790 603 1, 900 DNto 400 a a B.Z. Cataly 7, 7006, 300 8, 200 8, 400 None 4, 000 Dbio 6, 400

a a Product Properties:

Melt Index, g./ Min 1. 72 1. 56 1. 7 1. 65 2.03 1. 31 2. 6 1. 7 Density0. 9237 0. 9250 O. 9250 0. 9255 0. 930 0. 920 0. 920 0. 923 Stiffness,p.s.i 18, 000 19, 000 21, 000 22, 700 31, 700 15, 700 15, 300 18, 500Vicat Softening Point, 0.--- 9 98 100 10 108 93.0 0 98 FilmTranspanency, Inches 160 240 220 200 230 40 4 60 Film Gloss, Percent 5972. 7 68 64 62 29. 9 16.4 48.8 Film Haze, Per-vent 6 4. 3 5 2 6 5 5 18.9 34. 9 8. 1 Film Blnr'kim! 4 4 3 2 3 2 2 3 The polyethylene productsproduced by the present invention are primarily sought for use in makinghighly transparent glossy film. The film is used in packaging newclothes and in making garment bags for use by the dry cleaning industry.The film has better impact strength than the so-called medium and highdensity polyethylenes. It also has the ability to be easily drawn downto a thin film at high production rates. The extremely glossy appearanceand high transparency lend eye-appeal to the materials that are coveredby it. The products made by the process of this invention show a bettercombination of the above properties than any polyethylene products nowavailable.

Although the invention has been described in considerable detail withparticular reference to certain preferred embodiments thereof variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove, and as defined in the appendedclaims.

This application is a continuation of application Serial No. 861,453,filed December 23, 1959, and now abandoned.

We claim:

1. A process for the polymerization of ethylene which comprisesinitially partially polymerizing ethylene in the presence of caprylylperoxide catalyst at a temperature within the range of about 130 toabout 190 C. and then further polymerizing said ethylene at atemperature, above the said temperature and Within the range of about190 to about 270 C., the pressure throughout said polymerization beinggreater than about 500 atmospheres.

2. Process for the polymerization of ethylene which comprises conductingsaid polymerization in two zones at a temperature in the range of about130 to 250 C., the catalyst in the first zone being caprylyl peroxide,the temperature in said zone being substantially less than that in thesecond zone, and the pressure throughout said polymerization beinggreater than about 500 atmospheres.

3. Process for the polymerization of ethylene which comprises conductingthe polymerization in two separate zones in the presence of caprylylperoxide as the catalyst in the first zone at a temperature in the rangeof about 130 to about 190 C., the temperature in the other zone beingabove the said temperature and within the range of caprylyl peroxidecatalyst at a temperature within the range of about to about 190 C. andthen further polymerizing said ethylene in the presence of ditertiarybutyl peroxide catalyst at a temperature above the said temperature andwithin the range of about 190 to about 270 C., the pressure throughoutsaid polymerization being greater than about 500 atmospheres.

5. Process of claim 1 in which the caprylyl peroxide is introduced inconcentrations of 5 to 50 Weight percent in an inert organic solvent.

6. Process of claim 2 in which the caprylyl peroxide is introduced inconcentrations of 5 to 50 weight percent in an inert solvent.

7. Process of claim 1 in which the temperature range in the initialpolymerization is about to about 190 C. and the temperature of thefurther polymerization is in the range of about 190 to about 250 C.

8. Process of claim 4 in which the temperature range in the initialpolymerization is about 150 to about 190 C. and the temperature in thefurther polymerization is in the range of about 190 to about 250 C.

9. Process of claim 1 in which the temperature in the initialpolymerization is about 175 C., the temperature in said furtherpolymerization is about 255 C., and the pressure is about 1120atmospheres.

10. Process of claim 1 in which the temperature in the initialpolymerization is about C., the temperature in said furtherpolymerization is about 260 C., and the pressure is about 1160atmospheres.

11. Process of claim 5 in which the temperature in the initialpolymerization is about C,. the temperature in said furtherpolymerization is about 255 C., and the pressure is about 1120atmospheres.

12. Process of claim 6 in which the temperature in the first zone isabout 175 C., the temperature in the other zone is about 255 C., and thepressure is about 1120 atmospheres.

References Cited by the Examiner UNITED STATES PATENTS 2,964,515 12/60Rader 260-94.9 2,520,959 9/50 Powers 26092.8

JOSEPH L. SCHOFER, Primary Examiner.

1. A PROCESS FOR THE POLYMERIZATION OF ETHYLENE WHICH COMPRISESINITIALLY PARTIALLY POLYMERIZING ETHYLENE IN THE PRESENCE OF CARPYLYLPEROXIDE CATALYST AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 130* TOABOUT 190*C. AND THEN FURTHER POLYMERIZING SAID ETHYLENE AT ATEMPERATURE, ABOVE THE SAID TEMPERATURE AND WITHIN THE RANGE OF ABOUT190* TO ABOUT 270*C., THE PRESSURE THROUGHTOUT SAID POLYMERIZATION BEINGGREATER THAN ABOUT 500 ATMOSPHERES.